Forced choice tests started out as a clinical malingering tool (known as the Symptom Validity Test) detecting whether psychological symptoms were fake or genuine. In deception detection the forced choice paradigm tests for hidden knowledge of crime relevant detail in suspects. In this paradigm a suspect is presented with a questions, for example “What was the murder weapon” and two equally plausible answer alternatives, such as “gun” and “knife”. The suspect is instructed to select the correct answer alternative or guess if they don’t know it. Truth tellers, who by definition are unaware of the correct response, have to guess on each question and therefore their total score falls within levels of chance. Empirical evidence suggests, that liars faced with this paradigm purposefully select incorrect answers, providing total scores lower than expected by chance. This is known as underperformance and is used to determine deception.

My talk shall begin with a brief introduction to Signal Detection Theory as a measure of Accuracy in psychological tests and then introduce my research project. It focuses on the different strategies liars adopt to defeat the test. To do so my team and I propose a new theoretical model that distinguished strategies based on the beliefs formed over the test mechanism. I will present a summary of my recent studies illustrating this model and in addition, I will present a specific experiment wherein, we address the issue of coaching and countermeasures in this test. Finally, my talk will end on a reflection on practical applications and the question how to determine cut off points.